It’s time to come clean! Compared with cars, trucks and planes, the world’s ships rely on a particularly dirty form of fuel. Ship engines use what is known as heavy oil, a mixture of hydrocarbons with sulphur and nitrogen compounds. “Heavy oils are the highly viscous black residues from crude oil refining,” explains Anton Jell, Vice President Business Development at Linde Engineering. When used in a ship’s engine, they produce carbon dioxide as well as considerable amounts of sulphur and nitrogen oxides – emissions which are damaging to both human health and the environment. An International Maritime Organization (IMO) agreement has been reached to significantly restrict the use of these fuels in the near future. In late 2016, the IMO imposed a 2020 cap on marine fuel sulphur content, reducing it from today’s level of 3.5 percent down to 0.5 percent. “Refineries will face a tricky situation from that point onwards – they will no longer be able to sell their heavy oil as marine fuel if the ships have not been retrofitted with costly exhaust gas treatment devices,” says Jell. “But with our hydrogen technologies, we can offer refineries a solution that enables them to continue to valorise crude residue while also recovering other useful by-products.”

The shipping industry needs greener fuels, which poses a major challenge for refineries. Linde Engineering offers new solutions with its hydrogen plants.

Sulphur removal

Hydrogen (H2) is already indispensable for refining operations. Companies use this gas to remove sulphur from the fuels they produce in a chemical separation process called hydrodesulphurisation. In this reaction, H 2 bonds with sulphur to form hydrogen sulphide, which is captured and further processed in another treatment step. “The sulphur content is an indicator of the quality of the crude oil. This determines the process steps that are required in a refinery,” continues Jell. ‘Sweet’ or low-sulphur feedstock makes it easier to produce fuels like petrol, diesel, kerosene or heating oil. More processing is needed, on the other hand, for ‘sour’, or highly sulphurous crude oil – which means that more hydrogen is also needed.

Recovering hydrogen from heavy oil

Linde offers a process technology to recover hydrogen from heavy oil, as Jell explains: “Partial oxidation, or POX for short, is how we process heavy oil or refinery by-products like bitumen or pitch.” For this, the feedstock is heated to temperatures of around 1,400 degrees Celsius and oxygen is added to support sub-stoichiometric conversion. The resulting synthesis gas is then further conditioned. “With the POX process, we can withdraw as much hydrogen from the heavy oil as possible. This makes our technology an interesting option for oil companies seeking to derive maximum value from their residues in future,” maintains the Linde Engineering expert.

Hydrogen and pressure swing adsorption plant in Leuna, Germany.

H2 – bright prospects

Another advantage of the POX process is the fact that refineries can put the hydrogen they recover from heavy oil to good use. This is a valuable opportunity given the large volumes of this gas they need anyway – to desulfurize their fuel products for instance. “Much of the H2 produced globally is used to desulfurize fuel products so it is already making a key contribution to lower-pollution fuels. And with the trend towards stricter environmental regulations, demand for H2 is sure to remain on an upward path,” according to Jell. He and his team are engaged in concrete discussions with several leading oil companies. “For these potential megaprojects, we are working closely with our colleagues from Linde Gas, who would be able to operate the plants for customers on site,” points out Jell. The IMO cap means one thing above all for Linde’s engineering and gas specialists: the oil industry will need more hydrogen – regardless of how it is sourced.

Steam reforming – the industry standard for hydrogen production

Partial oxidation (POX) is the ideal process for obtaining hydrogen from heavy oil. However, the most common method currently used to produce H2 is steam reforming. A light hydrocarbon, usually natural gas, is used as the feedstock. Its main component methane (CH4) contains more hydrogen than any other hydrocarbon. In the steam reformer, steam and natural gas are catalytically cracked at temperatures in the region of 850 degrees Celsius. This forms a synthesis gas – a mixture of hydrogen, carbon monoxide (CO) and carbon dioxide (CO2). The carbon monoxide is converted into CO2 with steam in the downstream CO shift reaction, during which more hydrogen is produced. The H2-rich gas is finally purified to the desired quality level by means of pressure swing adsorption (PSA), membranes or cryogenic processes. Large steam reforming plants are currently able to produce more than 150,000 standard cubic metres of hydrogen per hour. To date, Linde has built over 300 H2 production plants around the world and has accumulated decades of experience in operating this technology.

Linde’s HyCO and ammonia plants supply Sadara Chemical Company in Al Jubail with hydrogen and other industrial gases.